This invention relates to a preheater for an engine, i.e., to a heater for the coolant of a liquid cooled engine. More particularly, this invention relates to an engine preheater of the lower radiator hose type.
For many years internal combustion engines, particularly automobile engines, that are called upon to operate at least part of the time in cold weather have been provided with engine preheaters or block heaters of the frost plug type to facilitate starting of the engines. This type of block heater ia essentially an immersion heater that is located in a frost plug opening in the block of an engine. The basic problem with frost plug type block heaters is that an extremely wide variety of them now must be manufactured and stocked if one is to be able to provide a block heater for every different automobile on the road. Thus, from 1963 to 1971 the number of different types of block heaters that would have to be provided just for the most popular makes of automobiles on the road has increased from 16 to 30.
Because of this problem a different type of engine preheater known as the lower radiator hose type has been developed. This type of engine preheater, as its name suggests, is connected in the radiator hose, and far fewer heaters of this type are required to be used with different makes of automobiles, since there are only a few standard sizes of radiator hoses.
However, prior art engine preheaters of the lower radiator hose type have in many instances been constructed with the heating element directly in the path of coolant flowing between the radiator and the engine. This can lead to overheating problems, particularly when the engine is operated during the summer months, since it is the practice to leave the engine preheater in the radiator hose at all times. In some designs this problem has been avoided by providing an enlarged peripheral well in the housing of the engine preheater and mounting the heating element in this well so as not to impede the flow of coolant through the device. However, this can lead to the problem of vapour lock. Furthermore, in engine preheaters of this type it has been common to fabricate the heating element itself of copper and the housing of the engine preheater of steel. This has led to problems of galvanic corrosion. There also is the problem of having to solder or braze the element in position.
In aforementioned application Ser. No. 321,455 there is disclosed an engine preheater that avoids the foregoing problems of it predecessors. This heater has a housing with a passage extending therethrough for passage of coolant through the heater. The housing has two end sections and an intermediate section, at least the latter being cast of heat conductive material and being located between the end section. The end sections are adapted to be connected to a radiator hose. An electric heating element is cast in place in and embedded in the intermediate section and is separated from the aforementioned passage by a part of the housing, whereby coolant flowing through the passage is inhibited from direct contact with the heating element but indirectly is heated thereby.
In a preferred embodiment a thermostat is located in heat transfer relationship with the housing on the side of the heating element remote from the passage. The thermostat is responsive to the temperature of the heating element for interrupting the supply of power thereto when the temperature sensed by the thermostat exceeds a predetermined upper limit. The thermostat is incorporated in a plug that is adapted for electrical connection to the heating element.
Further details of this engine preheater may be ascertained from the aforementioned applications, the disclosures of which are incorporated herein by reference.
After an engine preheater has been installed, the aforementioned plug normally is not removed. Operation of the preheater is obtained by plugging in to a conventional power outlet a plug at the other end of the line cord to the end that carries the plug that is connected to the heating element. Likewise, when the automobile or other device containing the engine having the preheater associated therewith is to be moved, or, in the case of a stationary engine, the preheater is to be disconnected, the former plug is disengaged from the power outlet. Consequently the plug that is connected to the heating element rarely is removed. However, it and the engine preheater are subject to vibration when the engine is operating and, in the case of an automobile or other vehicle, to additional vibration due to road shocks. In time these vibrations may impair the operating efficiency of the engine preheater by degrading the thermal connection between the housing of the engine preheater and the thermostat. It also might be possible for the plug that is connected to the heating element to become disconnected therefrom as a result of these vibrations or to become loose enough that oil, water, dirt or other contaminents that could cause a short circuit can find their way into the terminal box for the terminals of the heating element. The latter problem also is one that exists in the case where the plug that is connected to the heating element is removed for some time.